For those interested, 18650 cells are the way to go for rechargeable flashlights. The up-front cost is maybe 2x as much up front but will amortize quickly if your lights go through batteries quickly.
A lot of what makes a weapon light a weapon light these days is build construction. Two main things that come to mind are: solder/contact points in the body, and springs. If all the connections between the head assembly and the tailcap are solid, and the battery contacts are springs, it's going to be much more reliable as a weapon light than anything made 10 years ago.
Make sure the LED assembly is not gaining negative current through the body solely through ball solder - that assembly needs good heat dissipation through a metal head or it will die quickly, and solder contacts will also result in a quick percussive death.
Also, metal lamp heads are far superior to anything else due to heat dissipation. Those $20 80 lumen Brinkmann lamps are bright and very similar in output/function to the $60 Surefire G2L, but I've had two die on warm summer evenings on me - I suspect due to their plastic heads.
I posted a lengthy thread about this some time back; look through the archives if you're interested.
The Ultrafire lights and/or body parts seem to be of pretty good quality. I like getting the cheap knock-off crap (which works pretty well, again) from dealextreme.com
